The object of the invention is a modular device for the reception, the acquisition and the transmission to a central control and recording station of seismic and acoustic signals in a liquid medium, for use in marine seismic prospecting operations.
With respect to the marine seismic prospecting field, systems for the acquisition and the transmission of seismic signals are contained in sheaths which often have a length of several kilometers and are known as seismic streamers. Seismic streamers are towed under water by a ship along a seismic profile to be explored. Seismic streamers comprise a large number of successive sections interconnected by rigid boxes. Seismic receivers or sensors, each one consisting for example of one or several hydrophones, are distributed along each section. These receivers are connected with an acquisition device located in an interconnection box for sampling, digitizing and storing all the received signals. The different acquisition devices are generally connected with the central laboratory on the ship through common transmission lines divided in two groups. The first group known as outward lines transmits orders or commands addressed to the different devices in the laboratory. A second group known as inward lines transmits to towards the laboratory of the responses of the different devices and notably of the data stored at the end of each seismic emission and reception cycle. A seismic streamer is described for example in French Patent 2,471,088 (U.S. Pat. No. 4,398,271).
The current trend is to lengthen the seismic streamers and to increase the total number of receivers. This allows reduction of the intertrace which is the interval between two adjacent locations of the surveyed seismic profile and an increase in the sharpness of the recording, through the combining and the processing of the recorded signals.
Increasing the number of receivers in each streamer section requires to increasing the integration density of the components of the receivers. The presence of relatively heavy boxes between sections full of a liquid providing a certain buoyancy has the effect of bending the streamer out of shape. The drag of the streamer increases which induces parasitic signals which superpose on the wanted signals.
The length of the connections between the receivers and the acquisition devices, which may reach several ten meters, increases their sensitivity to the noise signals. A solution to the problem caused by the lengthening of the streamers and the resultant increase in the mass of the boxes is described in French Patent 2,590,684 (U.S. Pat. No. 4,787,069) which discloses a streamer having each seismic receiver closely associated with an electronic module for the purpose of adapting the analog signals supplied by the receivers.
The complexity of streamers having a high integration density poses another problem regarding the particular conditions of use imposed by the operators. The structure of highly integrated streamers is often too rigid and makes difficult adapting to operating conditions that had not been anticipated from the outset making usage difficult if not impossible and their cost considerable.